1. Field of the Invention
The present invention relates to improved knife blade apparatus for severing rupture disks, and more particularly, but not by way of limitation, to an improved knife blade apparatus adapted to be installed in a rupture disk assembly.
2. Description of the Prior Art
Rupture disk assemblies which include knife blades for severing the rupture disks upon the failure thereof have been developed and used heretofore. For example, U.S. Pat. No. 3,294,277 issued to Wood on Dec. 27, 1966, discloses a reverse buckling rupture disk assembly including knife blade apparatus for severing the rupture disk. In operation of the assembly, when the reverse buckling rupture disk fails as a result of fluid pressure exerted thereon, it reverses itself, impales on the knife blades and is severed whereby full opening of the rupture disk without fragmentation is achieved.
In most of the prior rupture disk assemblies which include knife blades, the knife blades are comprised of four sharpened blade legs of equal length having the interior ends thereof connected together and having the exterior ends rigidly welded or bolted to the interior of an annular support member. This type of knife blade apparatus is expensive to manufacture and where the blades are welded directly to the support member, the heat of welding causes stresses to be set up in the blades which often result in cracks or fractures therein when the blades are subjected to the impact loads associated with the failure of rupture disks. In addition, after one or more rupture disks have been severed by the knife blades, the blades become dull and either require the entire knife blade apparatus to be replaced or a time consuming unbolting and bolting operation to be performed. Another problem associated with knife blades which are welded or bolted to a support member arises in applications where the fluids relieved through the rupture disk assembly are cold, cool upon expansion or are hot. Upon contacting the knife blades which are rigidly attached within the support member, such fluids cause rapid contraction or expansion of the blades which in turn brings about the breaking or cracking thereof. That is, when the rupture disk in such an assembly ruptures and is severed by the knife blades, cold or hot fluid flowing through and being relieved by the rupture disk assembly quickly cools or heats the knife blades causing the knife blades to rapidly contract or expand. This in turn often causes the knife blades to crack either in one or more of the blade legs or in one or more of the welds at the points of attachment of the blade legs to the support member.
The knife blade apparatus disclosed in U.S. Pat. No. 4,363,418 issued to Matz on Dec. 14, 1982, includes a groove and annular snap ring arrangement whereby the knife blades are removably attached to an annular support member and are free to expand or contract therein. While this apparatus overcomes the problems mentioned above associated with apparatus where the knife blades are rigidly welded or bolted into the support member, the knife blades of the Matz apparatus can inadvertently be installed upside down in the apparatus, and because of the use of a snap ring, the apparatus is relatively expensive to manufacture.
By the present invention an improved knife blade apparatus adapted to be installed in a rupture disk assembly is provided whereby the knife blades of the apparatus are removable, they cannot be installed upside down, the apparatus is relatively inexpensive to manufacture and the knife blades are free to expand or contract while attached to the support member.